Three children developed allergic bronchopulmonary aspergillosis (ABPA) as a complication of either asthma or cystic fibrosis (CF). The first patient was a 14-year-old boy with CF who presented with an episode of haemoptysis and a decrease in lung function. He was initially treated with intravenous antibiotics but there was no improvement of his lung function. After starting prednisone-itraconazole his condition improved substantially. The second patient was a 16-year-old girl with CF complicated by ABPA. She was treated for 2 years with prednisone-itraconazole. Although the symptoms worsened when the prednisone dosage was gradually reduced, her growth retardation and increased weight decided us to stop prednisone treatment. Two years later, her CF was once again complicated by ABPA. The third patientwas a 16-year-old boy with asthma who had initially been treated for an asthma exacerbation. In retrospect, the cause of his pulmonary exacerbation was probably an ABPA episode. These cases illustrate how important but also how difficult the early diagnosis of ABPA is, and the dilemmas faced in treatment to prevent the fibrotic end stage.